1. Field of the Invention
The present invention relates to a microwave plasma process apparatus that utilizes microwaves so as to carry out a predetermined plasma process, specifically to a microwave plasma process apparatus that supplies microwave power to plasma in a process chamber through electromagnetic wave coupling.
2. Description of the Related Art
In plasma processes for fabricating semiconductor devices, liquid crystal displays (LCD), and the like, radio frequency (RF) waves and microwaves are used so as to discharge or ionize a process gas in a vacuum process chamber. An RF plasma apparatus mainly employs capacity coupling where a pair of electrodes is located, one electrode in parallel with the other leaving an appropriate gap between the electrodes in the process chamber. The RF waves are applied to one of the electrodes through a capacitor while the other electrode is grounded. However, it is difficult to produce high density plasma at relatively low pressures in the RF plasma apparatus. In addition, it is disadvantageous in that device elements on a wafer are more frequently damaged during the plasma process because the RF plasma inherently has high electron temperatures.
In contrast, the microwave plasma apparatus is advantageous in that the microwaves can produce high density plasma with low electron temperatures at relatively low pressures. Additionally, the microwave plasma apparatus has another advantage in that the microwave plasma can be efficiently produced in a two-dimensional large area at a wider pressure range when a planar microwave introduction window through which the microwaves are introduced into the chamber is employed. Moreover, the microwave plasma apparatus may have a simple configuration as a whole because a magnetic field is not required (see Patent Document 1).
Patent Document 1: WO2005/045913 A1 (FIG. 1(A), FIG. 2)
In a microwave plasma process apparatus, since microwave plasma is generated from a process gas by introducing microwaves and the process gas into the process chamber, the ways of introducing the microwaves and the process gas may be important factors that determine plasma characteristics and apparatus performance.
In the microwave plasma apparatus employing the planar microwave introduction window, there are two types of configurations in terms of introducing the process gas into the chamber. A first configuration has a shower plate serving as the microwave introduction window that opposes a susceptor. In this configuration, the process gas is ejected downward through plural gas ejection holes uniformly distributed in the shower plate.
On the other hand, a second configuration has one or plural gas ejection holes formed in a side wall of the chamber in order to eject the process gas inward to a plasma region in the chamber.
In the first configuration, while it is advantageous in that the plasma can be uniformly produced above the susceptor, the plasma density tends to be lower, which leads to a low etching rate when the plasma process apparatus is an etcher, and an inefficient process as a whole. This is because the shower plate having plural gas ejection holes provides a pathway through which the microwaves (electromagnetic waves) pass. In addition, such a configuration may cause a problem of contamination or the like.
On the other hand, in the second configuration, since the microwaves do not pass through the gas ejection holes made in the side wall of the chamber, abnormal discharging is unlikely to take place. However, it is difficult to diffuse the process gas uniformly in a radial direction, resulting in nonuniformly distributed plasma. Especially, since the chamber of a single-wafer plasma process apparatus is evacuated through a ring-like space between the susceptor and the inner wall of the chamber, the process gas tends to flow with nonuniform flow patterns in the chamber. This is because the process gas, which is introduced so as to flow over the ring-like space, is affected by a flow of gas headed toward an evacuation port below the ring-like space.
In addition, the process gas may be introduced into the process chamber through a gas ejection hole formed (pierced) through a dielectric window, which corresponds to a ceiling surface of the process chamber and opposes the susceptor.
In this case, since the dielectric window serves as a microwave introduction window, that is, as a microwave propagation path, there exists an electric field inside the dielectric window. Therefore, the process gas is exposed to the microwave electric field when flowing through the dielectric window, and thus may be ionized in a gas conduit in the dielectric window or near the gas ejection hole, which causes abnormal discharging. Such abnormal discharging may affect the dielectric window, so that the dielectric window is deteriorated or damaged in a relatively short period of time, and may impair process performance.
The present invention has been made in order to eliminate at least one of the above-mentioned disadvantages, and provides a plasma process apparatus that can prevent abnormal discharging in a microwave transmission line or radiation path, or a process gas ejection portion, so that plasma excellent in plasma density uniformity and controllability can be realized, thereby improving performance or quality of the plasma process.
In addition, the present invention may provide a plasma process apparatus in which plasma conditions or the plasma process can easily and efficiently be monitored.